Ionic thrusters use high voltage to ionize air and create an airflow, which in the right configuation can create thrust with no moving parts. I've tried an experiment like the above, and barely generated enough lift to raise a little balsa and aluminum foil off a table, but MIT says they can do far better.
From The Verge:
Stealth drones and other aircraft of the future could be powered by engines that don't have any moving parts, can't be detected by infrared, and are more efficient than what we have today. A new study by MIT researchers demonstrated all of these capacities and more for ionic thrusters and now at least one major aerospace company, Lockheed Martin, has said it's investigating the technology.
"I think UAVs would be the most likely initial application if [ionic thrusters] work," said the lead researcher in the study, MIT aerospace professor Steven Barrett, in an email to The Verge. Ionic thrusters for aircraft work by generating a high-voltage electrical field that strips electrons from air molecules, "ionizing" them and pushing them away behind an aircraft as ionic wind, to move the craft forward. Scientists and hobbyists have been tinkering with small, lightweight model planes using these kinds of propulsion systems since the 1960s. The technology uses no moving parts and is almost completely silent. It hasn't come to full-size planes, though, due to power concerns.
But scientists at MIT's department of aeronautics have built a working prototype (pictured above) that suggests the technology is more feasible than previously assumed, generating far more thrust (110 newtons per kilowatt of power) than a comparable jet engine (2 newtons per kilowatt). "You could imagine all sorts of military or security benefits to having a silent propulsion system with no infrared signature," said Steven Barrett, the lead author of the study published today in the journal Proceedings of the Royal Society. Indeed, Lockheed Martin is already expressing an interest, with an executive telling MIT News "there are still unanswered questions, but because they seem so efficient, it’s definitely worth investigating further."
Barrett told The Verge there are still major hurdles to overcome before aircraft ionic thrusters are able to be commercialized, namely a large enough power supply for their electrical field, and a way to retain efficiency at higher speeds. "At reasonable flight speeds [about 560 miles per hour] the efficiency does decrease, but still looks promising," he wrote in an email. Also, because it uses air molecules, "this kind of propulsion only works in an atmosphere," Barrett said. "It need not be the Earth's atmosphere though – for example, it could be useful in exploration of other planets where fully electric propulsion without moving parts may be beneficial."